1. Field of the Invention
The present invention relates to an apparatus for forming and extruding solid carbon dioxide blocks. More specifically, the present apparatus provides for the manufacture of solid carbon dioxide having consistent density throughout in a variety of different shapes and sizes.
2. Description of the Prior Art
The basic process for fabricating solid carbon dioxide (dry ice) blocks from liquid carbon dioxide has long been known. First, liquid carbon dioxide is forced through a small nozzle and allowed to expand into a sealed chamber. Adiabatic expansion of the liquid carbon dioxide freezes it into a solid. The solid carbon dioxide then precipitates into the chamber as a fine carbon dioxide snow. (This process is commonly called "flashing.") The dry ice is then normally compressed into blocks of known weight for sale to consumers.
For instance, the apparatus described in U.S. Pat. No. 3,576,112, issued Apr. 27, 1971, to Frost et al, is a typical device. Liquid carbon dioxide is flashed into a closed chamber having a reciprocating ram and a perforated head. The solid and gaseous carbon dioxide present in the chamber after flashing are pushed by the ram through the perforated head, and the carbon dioxide gas is vented from the chamber. The remaining dry ice is then continuously compressed into usable blocks and ejected from the flashing chamber. Here, the device is continuous in that the block of dry ice being extruded actually forms a seal between the flashing chamber and the atmosphere. As the compressed dry ice is pushed from the chamber, new dry ice is packed in its place, thereby effectively sealing the flash chamber from the ambient environment.
Duron et al describe a continuous dry ice pelletizing apparatus which operates in a rotary fashion in U.S. Pat. No. 3,670,516, issued Jun. 20, 1972. In this device, the liquid carbon dioxide is flashed into a chamber which is located directly above an interior ring gear. The ring gear has openings extending radially therethrough which act as small extrusion chambers. A concentrically mounted pinion meshes with the teeth of the interior ring gear in a planetary fashion, which forces the dry ice into the radial openings in the ring gear. As the pinion makes its way around the interior of the ring gear, the falling dry ice from the chamber above is gradually extruded as pellets from the outer circumference of the ring gear.
U.S. Pat. No. 3,708,993, issued Jan. 9, 1973, to Hardt et al, describes an apparatus for forming carbon dioxide pellets of high density which readily break into small pieces, yet do not agglomerate during shipment. The object of this apparatus is diametrically opposed to that of the present invention in that the pellets formed by the apparatus are designed with the specific intent to crumble. The present invention, however, is designed to fabricate dry ice shapes which have consistent density and will have the tendency not to be frangible. The apparatus described by Hardt et al is of the reciprocating plunger type, and forms an extruded rod of dry ice having radiating projections extending from an axial core. The core of the extruded rod has oblique fracture lines which extend completely around the core. The rod has a high density, yet will readily shatter into smaller pieces when forcibly struck. The rods are shipped intact, and then broken into smaller pieces by the end user, thereby avoiding agglomeration of the pieces during shipment.
Cann describes a dry ice extrusion apparatus which applies back pressure to the extruded dry ice in U.S. Pat. No. 4,033,736, issued Jul. 5, 1977, As discussed further below, gaseous carbon dioxide trapped within a solid extrusion causes the solid dry ice form to shattered due to the expansion of the trapped gas. The device described by Cann is a conventional extruder which applies contact pressure to an extruded dry ice rod immediately after it has been forced from the extruder. This allows the trapped carbon dioxide to diffuse from the rod, while the rod is prevented from shattering by the applied back pressure. The dry ice solid formed by the process, however, is not solid ice, but instead has a porous appearance.
U.S. Pat. No. 4,412,852, issued Nov. 1, 1983, to Umino et al describes an apparatus for producing brick shaped blocks of dry ice. The apparatus has two compartments, a pre-compression compartment located above a press mold compartment. In the upper pre-compression compartment, liquid carbon dioxide is flashed into carbon dioxide snow, and then pressed into a loose brick to drive off trapped gaseous carbon dioxide. The pre-compressed block is then dropped through a shuttered passageway to the press mold, where it is fully compressed into a dry ice brick. The apparatus does not allow for the formation of various shapes of dry ice forms, but only make dry ice bricks.
Yet another apparatus for fabricating dry ice shapes, this time into discs, is described in U.S. Pat. No. 4,780,119, issued Oct. 25, 1988, to Brooke. Here, an extruder forces dry ice snow through a fixed die. The pellets so produced are then gravity fed into a hydraulic forming chamber where the extruded pellets are compressed into discs. The apparatus described in this reference has a fixed die, and can therefore produce dry ice units of only one shape.
Spivak et al describe an apparatus for both making and delivering dry ice pellets in U.S. Pat. No. 5,249,426, issued Oct. 5, 1993. In this device, a rotary extruder compresses dry ice into pellets, which fall into a hopper at the bottom of the device. Gaseous carbon dioxide recovered under pressure from the extruder is then used to propel the dry ice pellets along a conduit to a movable container or storage tank.
U.S. Pat. No. 5,257,503, issued Nov. 2, 1993, to Rhoades et al describes an apparatus for the low pressure formation of dry ice units. High density dry ice bricks are formed by first introducing liquid carbon dioxide into a mold at a first low pressure for a selected period of time. Liquid carbon dioxide is then introduced into the mold at a higher pressure for a second period of time. The carbon dioxide introduced at the lower pressure forms a very light dry ice snow, which partially fills the mold. The carbon dioxide introduced at the higher pressure remains a liquid for a sufficient amount of time to saturate the low density snow already present in the mold. When this liquid carbon dioxide becomes solid due to the adiabatic expansion of part of the carbon dioxide, the liquid carbon dioxide-saturated dry ice solidifies into a high density dry ice brick. The dry ice brick so formed is not extruded in any manner.
U.S. Pat. No. 5,301,509, issued Apr. 12, 1994, to Lloyd et al describes an apparatus for producing dry ice particles for dry ice particle sand blasting. Dry ice is first liquefied and then transported via a snow barrel to a plurality of die openings. The liquid carbon dioxide is the converted back into dry ice by back pressure on the die. Forward pressure from super viscous liquid carbon dioxide entering the die openings forces the newly formed dry ice pellets out of the dies and into a transportation stream where they are carried to an application nozzle for sand blasting.